We propose to investigate the potent neurotoxins produced by the marine dinoflagellate Gonyaulax tamarensis, the organism responsible for the red tides along the Atlantic coasts of the U.S. and Canada, and of the coastal waters of countries bordering the North Sea. The organism is known to produce saxitoxin as well as several as yet uncharacterized toxins. We plan to grow the organism in laboratory culture, and isolate, purify and characterize its toxins. The toxins will also be isolated from scallops, which were exposed to a G. tamarensis red tide in the Bay of Fundy, and accumulated large amounts of the toxin. We further propose to investigate the chemistry of saxitoxin with the aim of preparing structural analogs, radiolabeled derivatives, and analogs that might serve for the development of affinity columns, and affinity labels for the localization, isolation, purification and characterization of the sodium channel in nerve membranes. Secondary objectives include the elucidation of the biosynthetic origin of saxitoxin, a better understanding of the environmental parameters affecting toxin production by the organism, the further refinement of toxin assay procedures, and a search for antidotes to these poisons.